1. Field of the Invention
The present invention relates to an organic electroluminescent element (hereinafter, also referred to as “organic EL element”, “luminescent element” or “element”), and particularly relates to an organic electroluminescent element excellent in emission characteristics and durability.
2. Description of the Related Art
Organic electroluminescent elements (organic EL element) have been extensively studied and developed in recent years because emission can be obtained with high luminance by driving at low voltage.
Generally, an organic EL element is composed of an organic layer including a luminescent layer and a pair of electrodes sandwiching the layer, and utilizes emission from excitons formed upon recombination, in the luminescent layer, of electrons injected through a cathode to holes injected through an anode.
The efficiency of the element has been improved advancing in recent years by using phosphorescent material. For example, iridium complexes and platinum complexes are known as disclosed in U.S. Pat. No. 6,303,238 and International Publication No. 00/57676. However, even such materials have not lead to the development of elements satisfying both high efficiency and high durability, and at present, there is demand for the development of a phosphorescent material meeting both high efficiency and high durability.